Thermoplastic resins, particularly polyolefin resins, are advantageous for having not only excellent moldability, heat resistance, mechanical properties and the like but also a low specific gravity and are, therefore, widely utilized in a variety of molded articles such as films, sheets and structural components.
Meanwhile, although polyolefin resins also have excellent electrical insulation properties, they have a problem of being easily electrically charged by friction and the like. When a molded article composed of a polyolefin resin is electrically charged, its outer appearance may be deteriorated due to generation of static electricity and attraction of dust and dirt in the surroundings. When the molded article is an electronic product, an electric charge may interfere with normal circuit operation. Moreover, there are also problems caused by electric shock. An electric shock to a person from a resin not only causes discomfort but also potentially induces accidental explosion in the presence of flammable gas or dust.
In order to solve these problems, resins are conventionally subjected to an antistatic treatment. A common antistatic treatment is addition of an antistatic agent to a resin of interest. Examples of the antistatic agent include coating-type antistatic agents that are applied to the surface of a resin molded article and kneading-type antistatic agents that are added when a resin is molded; however, the coating-type antistatic agents have problems of not only having poor persistence but also being wiped off when an object comes into contact with the surface.
From this viewpoint, conventionally, kneading-type antistatic agents have been examined and, for example, the use of a polyether ester amide has been proposed for the purpose of imparting antistaticity to polyolefin-based resins (Patent Documents 1 and 2). In addition, a variety of kneading-type antistatic agents, such as a block polymer having a structure in which a polyolefin block and a hydrophilic polymer block are repeatedly and alternately bound with each other, have been proposed (Patent Documents 3 to 5).
Moreover, in polyolefin resins, in addition to the above-described problem that, since polyolefin resins have excellent electrical insulation properties but easily generate and accumulate static electricity, dust and the like are likely to adhere to the surface and this often leads to a reduction in their commercial values, there are also problems of a long molding cycle, which is attributed to their slow post-molding crystallization rate, and a reduction in transparency and strength, which is attributed to generation of large crystals inside the resulting molded articles caused by progress of crystallization after heat-molding.
In order to improve these problems, conventionally, a nucleator (also referred to as “nucleating agent”, “crystallization accelerator”, “crystallizer”, “nucleophile” or “nucleus-forming agent”) is added for the purpose of increasing the crystallization temperature of the subject polyolefin resin and thereby allowing fine crystals to be rapidly formed during molding, and a kneading-type antistatic agent is also added for the purpose of imparting the subject polyolefin resin with long-lasting antistaticity (Patent Documents 6 to 8).